Aircraft carburetor



March 29, 1949. A. w. ORR, JR

AIRCRAFT CARBURETOR Filed Feb. 18, 1946 g Orr IN VEN TOR.

H TTOPNE Y Patented Mar. 29, 1949 AIRCRAFT CARBURETOR Andrew William Orr, Jr., Detroit, Mich., assignor to George M. Holley and Earl Holley Application February 18, 1946, Serial No. 648,301

7 Claims.

The object of this invention is to provide explosive mixtures which will be satisfactory when the pressure in the air entrance is above 30" of Hg, that is to say, at 40, 50, 60 and even '70" of Hg, which means that the air density is increased from A of a pound per cubic foot, which is normal at sea level, 30" Hg, to 7 A0, ,4 or 4 of a pound per cubic foot.

A further object is to combine this invention with the prior art in which barometric means are provided to correct the mixture ratio as air density in the air entrance falls from $1 to A to /40 pound per cubic foot or even less.

A further object of this arrangement is to secure correct metering in the air density range where the relationship of air flow versus metering differential can be expressed by the equation Wa= m by applying air density correction on the fuel differential side and by applying air density correction on the air difierential side in the range where the relationship of airflow to metering differential is more accurately expressed by the equation Wa=weight of air per second.

K1=constant depending on units used.

Kz=constant depending on units used.

d=density of the air.

Pt=Pressure in the throat of venturi.

Pe=Pressure in the air entrance. (These pressures are absolute, that is, they are read against a vacuum.)

K=Constant for air:1.406

Te -Temperature in air entrance (absolute).

This equals ordinary readings of a thermometer, plus 273 for C. and plus 460 for F.

A further object of this invention is to provide a carburetor having a density correction system such that the carburetor may be placed in between two stages of supercharging and all of the first stage pressure put on the carburetor entrance without afiecting the carburetor metering.

A further object of this invention is to provide a density compensation system such that better temperature compensation is obtained. Inasmuch as an air filled bellows gives perfect temperature compensation only at the fill density, the disclosed density correction system uses two or more bellows with each bellows being filled to a degree sufficient to give the best possible temperature correction over the portion of the density range wherein it is operating.

A further object of this invention is to provide a carburetor and a density correction system, such that the full value of the air metering differential is available for metering up to the point where compressibility enters into the square root relationship between airflow and metering differential. This makes possible a much larger carburetor for the same sea level metering differential, as low metering differential is one of the important limitations on carburetor size.

A further object of this invention is to provide a fuel metering system givin the highest possible absolute pressure on the fuel metering jets together with the lowest pressure drop through the carburetor.

This application is a continuation in part of the application filed April 14, 1945, Serial Number 588,359, now abandoned.

The figure shows all the essential elements of my invention.

In the figure, air enters at Ill through venturi H, flows past a small venturi l2, past a throttle l3 to the inlet to the supercharger. An air diaphragm I4 is provided with sealing diaphragms 59 and B0 of a well-known type, and is balanced against a fuel diaphragm l5 in a well-known manner.

In an equally well-known manner, a partiallyevacuated bellows l6 controls a valve I1, which valve ll admits a limited amount of air at the pressure of the air entrance l0 from an annular air chamber l8 through a pipe I 9 to the chamber 26 to the right-hand side (suction side) of the diaphragm l4. Impact tubes 51 and drain holes 58 are provided for obvious reasons.

A passage 2! is connected to the throat of the small venturi I2 and to the passage IS. A valve 22 admits suction to the chamber 20 and is controlled by a diaphragm 23, a spring 24 and an opposin sprin 41. At high suction in l2, there is automatically an increase in the area of the valve 22 between the pipe 2! and the passage l9. The chamber l8 communicates directly with the pressure chamber 25 to the left-hand side of the diaphragm M. The diaphragm 14 thus responds to air flow, and the efiect of air flow is corrected for changes in air density by reason of the evacuated bellows 16, which expands at high altitudes and is adjusted to cooperate with valve 22.

My invention consists in supplementing and to some extent substituting for the bellows IS another bellows 26, which is of a similar type to that of the partially-evacuated bellows l6, and like the bellows I5 is located in the air entrance so that it responds to the pressure and to a certain extent to the temperature of the entering air. The air enters the chamber surrounding the bellows 16 through an opening 5! and escapes through an opening t9. Air enters the chamber surrounding the bellows 20 through an opening 52 and escapes through an opening 50. The bellows 26 controls a valve 21, which admits fuel under pressure from the pipe 28, which is connected to a chamber 29 to the right-hand (pressure) side of the fuel diaphragm l5.

The chamber 29 communicates with a source of fuel under pressure 30 through a pipe 3!. The fuel flowing by the valve 2 descends through the pipe 32 through the chamber 33, which is the suction chamber on the left-hand side of the diaphragm l5, and descends through the restriction 34 to the fuel outlet 35, downstream of a main fuel restriction 35. The fuel flowing out of 35 flows by the loaded valve 3? along the passage 38, past the pressure-controlled valve as, to the fuel outlet 40, which delivers the fuel to the center of the supercharger in a well-known manner.

Servomotor valve ll controls the valve 3'? by controlling the pressure acting to the left of the diaphragm 42. The pipe 50 conveys fuel from this chamber Hi to the valve it. A passage l2, through the center of the valve Si, supplies fuel to the valve 4| Passage 83 connects the valve ll to the pipe 33. The pipe '45 to the left of the restriction 36 connects the chamber 35 with the chamber 54 to the right of the diaphragm Hill, which controls the valve 50. :25 is a spring imposing a load on the diaphragm 32 and thus on the valve Bl. The spring 53 supports the valve 3%.

Operation When excessive air flow takes place, the diaphragm I 4 moves to the right and the valve ll then permits fuel to flow from opening 58, through chamber M, along pipe 55, down pipe to pipe 38, past valve 39 to pipe t0, which permits the valve 3'! to open in a well-known manner. Hence the pressure drop due to the quantity of fuel flowing through restriction 35 is balanced against the drop in air pressure due to air flowing through the air entrance it, venturi l i and small venturi l2. When the valve 2? is opened, as it is when the air entrance pressure rises above that at approximately 11,000 feet, then fuel flows through the restriction 35 and also through the restriction 34.. The fuel flowing through restriction 36 is balanced against the air flowing through venturis II and i2. Hence the fuel flowing through restriction 34 around the bypass 20 2132 reduces th eifect of the pressure drop through 35, and to that extent renders the mixture richer than it otherwise would be. However, dense air automatically renders the mixture lean. Hence, this leanness is offset.

The value of this invention is that at high boost pressure in the air entrance, that is, the air pressure which would occur during a dive due to ramming action, will have a tendency with the orthodox fuel control means, such as the bellows id, to give a'lean mixture. When the air density in the air entrance is above .055 pound per cubic foot, bellows 26 in conjunction with the needle 2'! and restriction 34 increases the fuel dilferential across jet 35 compared with that of the fuel differential across diaphragm l5 and air difierential across diaphragm I l in such a manner as to compensate for the increased air density. Valve 27 operating in conjunction with bellows 26 can be opened to cover the increase in air density existing at 40", 50", 70" or even Hg or higher. Inasmuch as these high top deck pressures are used in a system where ram from a supercharger is applied to the carburetor entrance to obtain maximum amount of power, this carburetor imposes no restriction upon the military output of 'theengine because. the metering diiferential at the high airflows even'at very high entranc densities is sufficient for metering. Obviously, a condition might arise where the bellows 25 could be used without the bellows I5. For example, if a plane operated only at sea level or in the vicinity thereof.

Temperature correction In the operation of this device I have discovered that the best all around temperature correction is obtained when the air in the barometric element 26 has a density of .075 pound per cubic foot and the barometric element it has a density of .035 pound per cubicfoot. If another gas is used (such as nitrogen) a corresponding value would be given for the density of the gas inside the bellows. For example, with nitrogen the value would be .0725 for bellows 25 and for bellows I6 the value would be .0338. air is used the density in bellows 20 can have a range from .06 to .09 and in the bellows it from .025 to .055.

Further in the operation of this device I have discovered that it is best to arrange that when the pressur in the air entrance falls to 20 (mercury) that the bellows 25 should move valve 2? so as to close the passage 32. At this moment the valve l'l should begin to open as the bellows l5 expands. (This corresponds to an air entrance density of approximately .055 pound per cubic foot.) Under this condition the suction in the low pressure chamber 20 is equal to the suction in the throat of the venturi 52.

Now, I have further discovered that at an altitude corresponding to an air entrance density of .045 that the suction in chamber 20 should be approximately 75% of the suction in the venturi l2.

As higher air flows under these conditions the required suction in chamber 20 should'be reduced by about 1% but actually it falls off 3% in value if the opening around valve 22 was fixed in area. The mixture. thus would become slightly lean.

The opening around valve 22 is therefore increased in area as the diaphragm 23 rises sligl'ltly. .The increase'in area around valve 22 maintains 1. In a carburetor having an air entrance and a venturi therein, an air chamber, an air diaphragm therein, means for applying Venturi suction to one side of the diaphragm and atmospheric pressure to the other, a fuel chamber,-a fuel diaphragm therein, a fuel entrance, a fuel passage, a restriction therein, a passage connecting one side of the fuel diaphragm with the pressure on the upstream side of said fuel restric--- tion, a passage connecting the other side of'thefuel diaphragm with the downstream pressure.

In the cases where of said fuel restriction, means interconnecting the two diaphragms whereby the movement of one diaphragm opposes the movement of the other diaphragm, a fuel flow control valve located in series with said fuel restriction, operating means for said valve jointly controlled by the two opposing diaphragms whereby an increase in pressure difference across said fuel restriction tends to close the valve and an increase in the Venturi suction tends to open said valve so as to maintain a preselected fuel/air ratio, a bypass around said fuel restriction, a valve in said bypass, barometric means comprising an expansible chamber filled with gas and having flexible walls, a connection from the expansible chamber to said valve in said bypass, said expansible chamber being located in the air entrance so as to be responsive to the air entrance pressure when said pressure is greater than a preselected pressure between that of sea level and that corresponding to the pressure at which the relationship between airflow and Venturi suction no longer follows the square root proportional law, said barometric means being adapted to open said bypass valve in response to said air entrance pressure, a second barometric means comprising a second expansible chamber filled with gas and having flexible walls also located in said air entrance and a valve connected to said second expansible chamber of said second barometric means adapted to bleed air entrance air into the low pressure side of said air diaphragm when the air entrance pressure corresponds to an altitude greater than the altitude at which the first mentioned barometrically controlled valve ceases to operate.

2. A device as set forth in claim 1 in which the first mentioned barometric element is a bellows filled with air having a density of approximately .075 pound per cubic foot and in which the second barometric element is a bellows filled with air barring a density of approximately .035 pound per cubic foot.

3. A device as set forth in claim 1 in which the first mentioned barometric element is a bellows filled with air having a density between .06 and .09 pound per cubic foot and in which the second barometric element is a bellows filled with air having a density between .025 and .055 pound per cubic foot.

4. A device as set forth in claim 1 in which there is a valve located in the passage connecting said venturi and the low pressure side of the air diaphragms, a diaphragm connected to said valve, a passage admitting air at the air entrance pressure to one side of said diaphragm, the other side of said diaphragm being subjected to Venturi suction, yieldable means engaging with said diaphragm so as to oppose the pressure of the air in the air entrance acting against the Venturi suction.

5. A device as set forth in claim 1 in which the first mentioned barometric element is a bellows filled with air having a density of approximately .075 pound per cubic foot and in which the second barometric element is a bellows filled with air having a density of approximately .035 pound per cubic foot and in which there is a valve located in the passage connecting said venturi and the low pressure side of the air diaphragms, a diaphragm connected to said valve, a passage admitting air at the air entrance pressure to one side of said diaphragm, the other side of said diaphragm being subjected to Venturi suction yieldable means engaging with said diaphragm so as to oppose the air entrance pressure.

6. A device as set forth in claim 1 in which the first mentioned barometric element is a bellows filled with air having a density between .06 and .09 pound per cubic foot and in which the second barometric element is a bellows filled with air having a density between .025 and .055 pound per cubic foot and in which there is a valve located in the passage connecting said venturi and the low pressure side of the air diaphragms, a diaphragm connected to said valve, a passage admitting air at the air entrance pressure to one side of said diaphragm, the other side of said diaphragm being subjected to Venturi suction yieldable means engaging with said diaphragm so as to oppose the air entrance pressure.

7. Fuel control means for an airplane carburetor having an air venturi, an air diaphragm responsive to the depression created by the said venturi, a fuel supply under pressure, a fuel entrance, a fuel restriction therein, a fuel diaphragm responsive to the drop in pressure created by the restriction, a pilot valve operated by both of said diaphragms acting in opposition to each other, a fuel flow regulating valve located downstream from said fuel restriction, a third diaphragm connected to said fuel flow regulating valve, yielding means adapted to close said fuel flow regulating valve, a chamber adjacent to said third diaphragm, a restricted passage connecting said chamber with the fuel under pressure in said entrance, a passage leading out of said chamber through said pilot valve and returning to the downstream side of said fuel fiow regulating valve, a fourth diaphragm, a pressure regulating valve connected thereto and located downstream of said fuel flow regulating valve, yielding means ten-ding to open said pressure regulating valve, a chamber associated with said fourth diaphragm, the pressure in said chamber being adapted to close said pressure regulating valve, a passage connecting said last mentioned chamber with the downstream side of said fuel restriction whereby the pressure necessary to open said pressure regulating valve falls at high fuel fiows by an amount equal to the drop in pressure at said fuel restriction.

ANDREW WILLIAM ORR, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,367,499 Holley Jan. 16, 1945 2,378,036 Reggio June 12, 1945 2,394,664 Chandler Feb. 12, 1946 

